What would they spend their time doing while you coded?
The only caveat to this is if they've already exited and are successful entrepreneurs. My guess is they're not, and just looking for someone to do the development for free.
It'll really come down to me doing a lot of development between now and October, including managing another developer if they stay true to their word and get another developer to help out.
And no, they haven't already exited or anything of that nature. Not yet. Ambitious friends of mine, though.
It also sounds like you have goals of your own. There is a true opportunity cost here. This will be your side project for longer than you probably expect. You don't really get any others if you're trying to get a business off the ground. I'm not sure how old you are, but divide the remainder of your working life into 5 year chunks. That's how many tries you get, roughly speaking, if you're going the startup route.